1. Field of the Invention
The present invention relates to a method of preventing a peeling issue of a high stressed thin film, and more particularly, to a method that includes a multi-step pre-heating process for improving the temperature rising capability. Consequently, the peeling issue of the high stressed thin film is avoided.
2. Description of the Prior Art
Silicon nitride is known as a good dielectric material for its good dielectric and insulating characteristics, and has been widely used as the materials of interlayer dielectric, dielectric liner, passivation layer, and so on. However, the high stress of silicon nitride has always been a problem during semiconductor processes. The high stress makes the silicon nitride layer have a poor interface between itself and the layer in contact with the silicon nitride layer. Consequently, the silicon nitride layer tends to peel and leads to peeling and particle issues. The peeling issue gets serious while the temperature rising capability is poor. An STI process is exemplarily described thereinafter to illustrate the peeling issue and the particle issue of a high stressed thin film.
Please refer to FIG. 1. FIG. 1 is a flow chart of a conventional STI process. As shown in FIG. 1, the conventional STI process includes the following steps:
Step 10: providing a wafer having shallow trenches;
Step 12: forming a silicon nitride liner on the inner surface of the shallow trenches;
Step 14: performing a single-step pre-heating process on the wafer;
Step 16: performing an HDPCVD process to fill a silicon oxide layer into the shallow trenches; and
Step 18: performing a CMP process to remove the silicon oxide layer outside the shallow trenches.
The steps of forming STIs are detailed as follows. Please refer to FIG. 2 through FIG. 4. FIG. 2 through FIG. 4 are schematic diagrams illustrating a conventional STI process. As shown in FIG. 2, a wafer 20 is provided. Then, a pad oxide pattern 22 and a pad nitride pattern 24 are consecutively formed on the wafer 20. Subsequently, an etching process using the pad nitride pattern 24 as a hard mask is performed to form shallow trenches 26. Following that, a silicon oxide liner 27 and a silicon nitride liner 28 are respectively formed on the inner wall of the shallow trench 26.
The wafer 20 is then delivered to an HDPCVD chamber 30 for forming STIs. The HDPCVD chamber 30 includes a chamber body 32, an E-chuck 34 for supporting the wafer 20, a back-side cooling system 36, a bias RF power 38 coupled to the E-chuck 34, a plurality of inductive coils 40 and 42 respectively disposed on the top and sides of the chamber body 32, a top RF power 44 coupled to the inductive coils 40, and a side RF power 46 coupled to the inductive coils 42. The process temperature of an HDPCVD process is high, for example 700 Celsius degrees, and the wafer 20 has to be pre-heated in advance. Normally, a pre-heating process is performed to raise the temperature of the wafer 20 to about 500 Celsius degrees. During the pre-heating step, power is applied to the top RF power 44 and the side RF power 46, and gases such as oxygen or argon is implanted into the chamber body 32 to raise the temperature of the wafer 20.
As shown in FIG. 3, an HDPCVD process is then performed to fill a silicon oxide layer 48 into the shallow trenches 26. As shown in FIG. 4, a CMP process is performed to remove the silicon oxide layer 48 outside the shallow trenches 26 so as to form STIs 50.
The conventional pre-heating process is single step, and the wafer 20 is disposed on the E-chuck 34 while performing the pre-heating process, i.e. the wafer 20 is distant from the inductive coils 40 and 42 positioned overhead. Consequently, the temperature raising capability is insufficient. In addition, if a low pre-heating power is adopted, it takes more time to heat the wafer 20, and it is difficult to increase the temperature as desired. Under such a condition, the peeling issue of the silicon nitride liner 28 gets serious. On the other hand, if a high pre-heating power is adopted, it takes less time to heat the wafer 20 and the peeling issue of the silicon nitride liner 28 may be alleviated. However, the high pre-heating power enhances dropped particles, and leads to a particle issue. Therefore, the conventional method faces a dilemma of the peeling issue or the particle issue.